Method and device for locating a vehicle

ABSTRACT

A method for locating a vehicle involves detecting an elevation profile of a roadway of the vehicle and in which image features on the roadway are detected as landmarks and are compared with landmarks stored on a digital map. A transformation of the detected and/or stored landmarks into a common perspective performed to compare the landmarks. The transformation is carried out based on model parameters of a parametric model of the elevation profile of the roadway and a parametric model of a vehicle inclination. The model parameters are determined by determining an expected elevation profile of the roadway from the parametric models of the elevation profile and the vehicle inclination and minimizing a difference between the expected elevation profile and the detected elevation profile by varying the model parameters.

BACKGROUND AND SUMMARY OF THE INVENTION

Exemplary embodiments of the invention relate to a method for locating avehicle, a device for locating a vehicle, and a vehicle having such adevice.

From the prior art, it is known to compare and correlate data detectedby sensors about objects in the environment of a vehicle with theinformation stored on a digital map, which has features of the objectitself and position information associated with the respective object,in order to determine a position of the vehicle with the aid of thedigital map. By way of example, WO 2018/059735 A1 relates to a methodfor the self-localization of a vehicle, in which images of the vehicleenvironment are captured by means of at least one image capturing unitand image features are extracted from the ambient images andsuperimposed on environment features stored on a digital environmentmap.

Exemplary embodiments of the invention are directed to improvinglocalization of a vehicle, i.e., the determination of a position of avehicle.

In the method for locating a vehicle according to the invention, anelevation profile of a roadway of the vehicle is detected. For locating,image features on the roadway are detected as landmarks and comparedwith landmarks stored on a digital map. To make the landmarkscomparable, the detected and/or stored landmarks are transformed into acommon perspective.

Advantageously, the landmarks stored on the digital map are transformedinto the perspective of the detected landmarks, i.e., into theperspective of the vehicle. Through this transformation, the landmarksstored on the map are virtually projected onto the roadway. Virtuallymeans that the projected landmarks are only calculated. Through theprojection, the stored landmarks are thus calculated back into a form asthey would be seen from the vehicle and are thus comparable with thedetected landmarks.

Alternatively, the detected landmarks can also be transformed into theperspective of the stored landmarks, i.e., into the perspective of thedigital map. The perspective of the digital map is the perspective of atop view, i.e., a view from above. Through this transformation, thedetected landmarks are thus virtually projected into the plane of thedigital map. The detected landmarks are thus calculated back into a formas they would have to be stored on the digital map and are thuscomparable with the landmarks stored on the map.

In accordance with the invention, the transformation of the detectedand/or stored landmarks is performed based on model parameters of aparametric model of the elevation profile of the roadway and aparametric model of a vehicle inclination of the vehicle. The modelparameters are determined by determining an expected elevation profileof the roadway from the parametric models of the elevation profile andthe vehicle inclination and minimizing a difference between the expectedelevation profile and the detected elevation profile by varying themodel parameters.

Preferably, the method according to the invention is carried out withthe following steps:

-   -   detecting the roadway in the environment of the vehicle with a        first sensor unit of the vehicle,    -   determining the detected elevation profile of the roadway based        on first data of the first sensor unit,    -   determining the model parameters of the parametric models of the        elevation profile of the roadway and of the vehicle inclination,    -   recording second data representing the detected landmarks by the        first sensor unit or by a second sensor unit,    -   comparing the detected landmarks with the landmarks stored on        the digital map after transforming the detected and/or stored        landmarks into the common perspective, and    -   determining a position of the vehicle from the comparison of        landmarks.

The vehicle may be a car, lorry, bus, rail vehicle or aircraft.

Preferably, the parametric model of the vehicle inclination is definedsuch that it describes a deflection of a longitudinal axis andtransverse axis of the vehicle with respect to a reference plane, inparticular a horizontal plane.

Preferably, the parametric model of the vehicle inclination is generatedbased on a tangent function of a pitch angle of the vehicle around atransverse direction and a tangent function of a roll angle of thevehicle around a longitudinal direction. The pitch angle and the rollangle are thereby the model parameters of the parametric model of thevehicle inclination.

The longitudinal direction and the transverse direction are defined inparticular in a coordinate system that moves with a center of gravity ofthe vehicle, wherein the longitudinal direction and the transversedirection are located in a horizontal plane, and the longitudinaldirection moves with a yaw angle of the vehicle, i.e., azimuth withrespect to the earth, while the transverse direction remainsperpendicular to the longitudinal direction. The roll angle as well asthe pitch angle of the vehicle in each case are therefore defined inparticular with respect to this horizontal plane.

When determining the model parameters, a plurality of measurement pointsfrom the first sensor data is preferably used to determine a respectiveelevation of the elevation profile at the measurement points of theroadway. This plurality of respective elevations is compared to aplurality of points on the expected elevation profile, such that itresults in a system of equations, wherein the difference between thedetected elevation profile and the expected elevation profile is reducedby minimization, and ideally becomes zero by adjusting the modelparameters accordingly. This corresponds to a search for such modelparameters for which the difference from the detected elevation profileand the expected elevation profile becomes minimal based on theplurality of measurement points considered.

The reason why the expected elevation profile is generated from theparametric model of the elevation profile of the roadway and theparametric model of the vehicle inclination is that the parametric modelis defined relative to the roadway, wherein the vehicle inclination,i.e., the pitch angle and the roll angle, have an influence on whatelevation is actually detected by the first sensor unit of a respectivepoint on the roadway. The theoretically expected elevation profile,which indicates an expectation of the measurement from the first sensorunit, thus takes into account this influence of the pitch angle and theroll angle. Thus, not only are the model parameters adjusted, but theroll angle and the pitch angle are also determined such that theexpected elevation profile and the actual detected elevation profilematch as closely as possible.

The image features on the roadway are, in particular, markings that areapplied to the roadway in the environment of the vehicle, for examplelane markings, stop lines, direction arrows, characters, etc. However,it is also conceivable that other features present on the roadway aredetected and used as detected landmarks.

It is an advantageous effect of the invention that, when locating aposition of the vehicle, i.e., locating the vehicle by comparing thelandmarks, it is taken into account that roads are not always flat. Inparticular, roads may have a curved or distorted or bent surfacerelative to a reference ellipsoid of the earth. In addition to this, dueto the spring mounting of the vehicle, the vehicle may have a pitchangle or also a roll angle with respect to this reference ellipsoid,wherein these orientation angles are also taken into account in thetransformation. The transformation of the detected and/or storedlandmarks into a common perspective ensures that the detected and storedlandmarks are comparable with each other (because the landmarks storedon the map are typically defined by looking at the environment fromabove, while the detected landmarks are detected from the perspective ofthe vehicle, in particular from the perspective of the first or secondsensor unit). In this respect, the comparison of the landmarks iscorrected for errors caused by the curved surface of the road and alsoby the vehicle inclination (pitch angle and roll angle). The detectedlandmarks can thus be assigned with better accuracy to the landmarksstored on the digital map, which advantageously enables more preciselocating of the vehicle with the aid of the landmarks stored on thedigital map.

According to an advantageous embodiment, the first sensor unit is thesame as the second sensor unit, i.e., the roadway and the landmarks aredetected with the same sensor unit. Preferably, a stereo camera unit isused for both the first sensor unit and the second sensor unit. Furtheradvantageously, the determination of the detected elevation profile ofthe roadway based on the first data as well as the comparison of thesecond data with the landmarks stored on the digital map can beperformed by one and the same data set of first data and second data inone go. If the first data are equal to the second data, one image dataset of the stereo camera unit can be used for both purposes. This hasthe advantage that the method can be executed with relatively littlesensor data and with relatively little computational effort.

According to a further advantageous embodiment, the parametric model ofthe elevation profile of the roadway comprises a parametrizable curvefor the longitudinal direction and a parametrizable curve for thetransverse direction.

According to a further advantageous embodiment, the parametrizable curvefor the longitudinal direction is a second-order polynomial having twomodel parameters, and the parametrizable curve for the transversedirection is a fourth-order polynomial having four model parameters.

The second-order polynomial is preferably represented as: H(x)=ex²+fx,wherein e and f are the model parameters of the polynomial for thelongitudinal direction, which are determined, wherein x is a coordinatein the longitudinal direction.

The fourth-order polynomial is preferably represented asH(y)=ay⁴+by³+cy²+dy, wherein a, b, c, and d are the model parameters ofthe polynomial for the transverse direction, which are determined,wherein y is coordinate in the transverse direction.

The parametric model of the vehicle inclination is preferably expressed,based on the tangent function of the pitch angle and the tangentfunction of the roll angle as the term H_(e), by:

H_(e)=x*tan(pitch angle)+y*tan(roll angle), wherein pitch angle and rollangle are the model parameters to be determined, x is the coordinate inthe longitudinal direction and y is the coordinate of the transversedirection.

According to a further advantageous embodiment, minimizing thedifference between the expected elevation profile and the detectedelevation profile to determine the model parameters is performed bymeans of one of the following processes and methods:

-   -   Gauss-Newton method,    -   Levenberg-Marquard method,    -   gradient-based search method,    -   quadratic optimization,    -   training of a neural network,    -   genetic or evolutionary algorithm.

According to a further advantageous embodiment, a time series of thepitch angle and/or the roll angle is used to calibrate the first sensorunit and/or the second sensor unit respectively.

According to a further advantageous embodiment, at least one of thefollowing is used for the first sensor unit and/or the second sensorunit:

-   -   lidar unit,    -   radar unit,    -   stereo camera unit,    -   ultrasonic sensor unit.

Another aspect of the invention relates to a device for determining aposition of a vehicle, having:

-   -   a first sensor unit of the vehicle, wherein the first sensor        unit is designed to detect a roadway in an environment of the        vehicle,    -   a computing unit adapted to determine a detected elevation        profile of the roadway based on first data from the first sensor        unit, and designed to determine model parameters of a parametric        model of the elevation profile of the roadway and a parametric        model of the vehicle inclination by minimizing a difference        between an expected elevation profile and the detected elevation        profile, wherein the expected elevation profile is generated        from the parametric models of the elevation profile and the        vehicle inclination,    -   a second sensor unit designed to record second data representing        the detected landmarks,    -   wherein the computing unit is further adapted to compare the        detected landmarks with landmarks stored on a digital map,        wherein the detected and/or stored landmarks are converted to a        common perspective by a transformation to ensure comparability        of the landmarks, and wherein the transformation is performed        based on the determined model parameters of the parametric        models of the elevation profile and the vehicle inclination, and        wherein the computing unit is designed to determine a position        of the vehicle from the comparison of the landmarks.

Another aspect of the invention relates to a vehicle having a device asdescribed above and below.

Advantages and preferred developments of the proposed device emerge froman analogous and corresponding transfer of the statements made above inconnection with the proposed method.

Further advantages, features and details emerge from the followingdescription, in which—optionally with reference to the drawing—at leastone exemplary embodiment is described in detail. Identical, similarand/functionally identical parts are provided with the same referencenumerals.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Here are shown:

FIG. 1 schematically a method for determining a position of a vehicleaccording to an exemplary embodiment of the invention,

FIG. 2 a roadway having a vehicle located thereon in relation to theexecution of the method according to the exemplary embodiment of FIG. 1,

FIG. 3 a grid of measurement points on a roadway in relation to theexecution of the method according to the exemplary embodiment of FIG. 1, and

FIG. 4 a vehicle having a device according to a further exemplaryembodiment of the invention.

The representations in the figures are schematic and not to scale.

DETAILED DESCRIPTION

FIG. 1 shows a method for determining a position of a vehicle 10, i.e.,for locating the vehicle. Certain details of this method or of thesituation to which the method is applied can be seen from FIG. 2 andFIG. 3 , which also refer to the embodiments of FIG. 1 .

In the first step S1 of the method, a roadway in an environment of thevehicle 10 is detected with a first sensor unit 3 of the vehicle 10, thefirst sensor unit 3 being designed as a stereo camera unit. Next, adetected elevation profile of the roadway is determined based on thefirst data supplied by the stereo camera unit 3 (step S2). This is donefor a plurality of measurement points from the image of the stereocamera unit 3, as depicted in FIG. 3 . Here, the roadway is curvedaround a central line of the roadway, such that markings on the rightside of the roadway appear distorted downwards. For the plurality ofmeasurement points, determining S3 model parameters of a vehicleinclination H_(xy) of the elevation profile of the roadway and of modelparameters of a vehicle inclination H_(e) of the vehicle 10 ensues byminimizing a difference between an expected elevation profile H_(the)and the detected elevation profile. The expected elevation profileH_(the) is generated by summing the parametric model H_(xy) of theelevation profile of the roadway and the parametric model H_(e) of thevehicle inclination:H _(the) =H _(xy) +H _(e).

The parametric model of the elevation profile of the roadway is composedof a second-order polynomial H(x) having two model parameters e, f forthe longitudinal direction x, and of a fourth-order polynomial H(y)having four model parameters a, b, c, d for the transverse direction y:H(y)=ay ⁴ +by ³ +cy ² +dy;H(x)=ex ² +fx.

The parametric model of vehicle inclination describes the inclination ofthe vehicle relative to a reference plane, for example relative to ahorizontal plane. It is defined as a quantity H_(e) based on a tangentfunction of a pitch angle of the vehicle around a transverse directionand a tangent function of a roll angle of the vehicle around alongitudinal direction as follows:H _(e) =x*tan(pitch angle)+y*tan(roll angle).

Here, pitch angle and roll angle refer to the model parameters of theparametric model of the vehicle inclination, x represents the coordinatein longitudinal direction and y represents the coordinate in transversedirection.

The expected elevation profile H_(the) is formed based on the parametricmodels H_(xy), H_(e) by summing the models:H _(the) =H _(xy) +H _(e) =H(x)+H(y)+H _(e).

For a plurality of points assigned to the roadway and the respectivedetected heights H_(sen) at a respective measurement point of thedetected elevation profile, it is thus obtained:

r₁ = H_(the)(x₁, y₁) − H_(sen)(x₁, y₁)r₂ = H_(the)(x₂, y₂) − H_(sen)(x₂, y₂)r₃ = H_(the)(x₃, y₃) − H_(sen)(x₃, y₃) …

Minimizing the difference between the expected elevation profile and thedetected elevation profile, expressed by the residuals r₁, r₂, r₃, isdone to determine the model parameters by means of theLevenberg-Marquard method, such that the model parameters a, b, c, d, e,f, pitch angle, and roll angle are obtained. In this way, a mathematicaldescription of the current elevation profile and the current vehicleinformation is obtained.

This is followed by the detection S4 of second data on objects from theenvironment of the vehicle 10 by the second sensor unit 5, that is, thestereo camera unit, which corresponds to the first sensor unit 3. Thesecond data represent the detected landmarks. Furthermore, thecomparison S5 of the second data, i.e., the detected landmarks, withlandmarks stored on a digital map follows, wherein the stored landmarksare transformed into the perspective of the detected landmarks beforethe comparison. The transformation is based on the determined modelparameters of the parametric models of the elevation profile and thevehicle inclination. Its purpose is to transform the stored landmarksinto a form in which they can be compared with the detected landmarks.Finally, determining S6 a position of the vehicle 10 from the comparisonof detected landmarks with the stored landmarks transformed into thesame perspective occurs. It is also conceivable that, in step S5, thedetected landmarks are transformed into the perspective of the storedlandmarks before being compared. Accordingly, in step 6, the position isthen determined from the comparison of the transformed detectedlandmarks with the stored landmarks.

FIG. 2 shows, in addition to FIG. 1 , the kinked course of the road onwhich the detected landmarks appear kinked downwards from the point ofview of the stereo camera unit 3.

FIG. 3 shows a possible grid of measurement points for comparing theexpected with the measured elevation profile, as well as the orientationof the longitudinal direction x and the transverse direction y.

FIG. 4 shows a vehicle 10 having a device 1, wherein the device 1 servesto determine a position of a vehicle 10, having:

-   -   a first sensor unit 3 of the vehicle 10, wherein the first        sensor unit 3 is designed to detect a roadway in an environment        of the vehicle 10,    -   a computing unit 7, configured to determine a detected elevation        profile of the roadway based on first data from the first sensor        unit 3, and designed to determine model parameters of a        parametric model of the elevation profile of the roadway and a        parametric model of the vehicle inclination by minimizing a        difference between an expected elevation profile and the        detected elevation profile, wherein the expected elevation        profile is generated from the parametric models of the elevation        profile and the vehicle inclination,    -   a second sensor unit 5, designed to detect second data on        objects from the environment of the vehicle 10 representing the        detected landmarks,        wherein the computing unit 7 is further designed to compare the        detected landmarks with landmarks stored on a digital map,        wherein the detected or stored landmarks are converted to the        same perspective by a transformation to enable the comparison of        the landmarks, and wherein the transformation occurs based on        the determined model parameters of the elevation profile and the        vehicle inclination, and wherein the computing unit 7 is        designed to determine a position of the vehicle 10 from the        comparison of the landmarks.

Although the invention has been further illustrated and explained indetail by preferred exemplary embodiments, the invention is not limitedby the disclosed examples and other variations can be derived therefromby those skilled in the art without departing from the scope ofprotection of the invention. It is therefore clear that a plurality ofpossible variations exist. It is also clear that exemplary embodimentsmentioned are really only examples, which are not to be understood inany way as limiting, for example, the scope of protection, the possibleapplications or the configuration of the invention. Rather, thepreceding description and the description of figures enables the personskilled in the art to implement the exemplary embodiments in a concretemanner, wherein the person skilled in the art, being aware of thedisclosed idea of the invention, can make a variety of changes, forexample with respect to the function or the arrangement of individualelements mentioned in an exemplary embodiment, without leaving the scopeof protection defined by the claims and their legal equivalents, such asfurther explanations in the description.

The invention claimed is:
 1. A method for locating a vehicle on aroadway, the method comprising: detecting, by a first sensor unit of thevehicle, the roadway in an environment of the vehicle to generate aplurality of measurement points; detecting an elevation profile of theroadway in the environment of the vehicle based on the plurality ofmeasurement points; determining a set of parametric models, whichincludes a first and second parametric model, wherein the firstparametric model is of the detected elevation profile of the roadway andcomprises (1) a parameterizable curve for a longitudinal direction ofthe detected elevation profile, and (2) a parametrizable curve for atransverse direction of the detected elevation profile, and the secondparametric model is of an inclination of the vehicle and has pitch angleand roll angle as parameters; determining an expected elevation profileof the roadway based on the set of parametric models; determiningparameters of the first and second parametric models, including thepitch angle and roll angle parameters, by minimizing a differencebetween the expected elevation profile and the detected elevationprofile; detecting, by a second sensor unit, landmarks in theenvironment of the vehicle; transforming, using the determinedparameters of the first and second parametric models, one of thedetected landmarks or the landmarks stored on the digital map into acommon perspective with the other one of the detected landmarks or thelandmarks stored on the digital map; and comparing, using the commonperspective, the detected landmarks with landmarks stored on the digitalmap to determine a position of the vehicle; and determining a positionof the vehicle based on the comparison of the detected landmarks withthe information from the digital map.
 2. The method of claim 1, whereinthe parametrizable curve for the longitudinal direction is asecond-order polynomial having two model parameters, and theparametrizable curve for the transverse direction is a fourth-orderpolynomial having four model parameters.
 3. The method of claim 1,wherein the parametric model of the vehicle inclination describes adeflection of a longitudinal axis and transverse axis of the vehiclewith respect to a contact area of the vehicle with the roadway.
 4. Themethod of claim 3, wherein the parametric model of the vehicleinclination is generated based on a tangent function of a pitch angle ofthe vehicle and a tangent function of a roll angle of the vehicle. 5.The method of claim 4, wherein a time series of the pitch angle and/orthe roll angle is used to calibrate the first sensor and/or the secondsensor, respectively.
 6. The method of claim 1, wherein the first sensorunit or the second sensor unit comprises at least one of: lidar unit,radar unit, stereo camera unit, and ultrasonic sensor unit.
 7. Themethod of claim 1, wherein the first sensor unit and the second sensorunit are a same sensor unit.
 8. The method of claim 7, wherein the samesensor unit is a stereo camera.